Be honest, no argument would persuade you because you are coming from a negative perspective. Other have offered different viewpoints to you, and you have rejected them all. So again, attempting to persuade you is a waste of time. You are entitled to your opinion, but so are others entitled to theirs.
I have suggested that he might have other reasons: he is perhaps well ahead in internal polling and sees no reason to risk a debate. I agree he might be negotiating this way.
As of now, with the polling the way it is and the state of play therefore adverse to Trump, I disagree with the decision, if final, to boycott the debate.
By the way good news Fox just came up with 49/48 Trump in Arizona.